A team of researchers has discovered bulk superconductivity at 38 K in the iron arsenide compound (Ba1−xKx)Fe2As2 with x ≈ 0.4. This compound, which has a ThCr2Si2-type structure, is doped with potassium ions to introduce holes into the (FeAs)− layers, suppressing a spin density wave (SDW) anomaly and inducing superconductivity. This finding is significant as it represents the highest critical temperature (Tc) observed in hole-doped iron arsenide superconductors so far. The study shows that superconductivity in these systems arises primarily from the (FeAs)− layers and may occur in other related compounds. The research expands the class of superconductors to oxygen-free compounds with the ThCr2Si2-type structure, similar to recently discovered arsenide-oxide superconductors. The parent compound BaFe2As2 is a poor metal with a SDW anomaly at 140 K, but hole doping suppresses this anomaly and leads to superconductivity. The study also confirms bulk superconductivity through measurements of electrical resistance and magnetic susceptibility, showing a sharp drop in resistance at 38 K, indicating superconductivity. The results suggest that hole doping is a viable pathway to achieve high-Tc superconductivity, particularly in oxygen-free compounds. This discovery opens new avenues for the development of high-temperature superconductors.A team of researchers has discovered bulk superconductivity at 38 K in the iron arsenide compound (Ba1−xKx)Fe2As2 with x ≈ 0.4. This compound, which has a ThCr2Si2-type structure, is doped with potassium ions to introduce holes into the (FeAs)− layers, suppressing a spin density wave (SDW) anomaly and inducing superconductivity. This finding is significant as it represents the highest critical temperature (Tc) observed in hole-doped iron arsenide superconductors so far. The study shows that superconductivity in these systems arises primarily from the (FeAs)− layers and may occur in other related compounds. The research expands the class of superconductors to oxygen-free compounds with the ThCr2Si2-type structure, similar to recently discovered arsenide-oxide superconductors. The parent compound BaFe2As2 is a poor metal with a SDW anomaly at 140 K, but hole doping suppresses this anomaly and leads to superconductivity. The study also confirms bulk superconductivity through measurements of electrical resistance and magnetic susceptibility, showing a sharp drop in resistance at 38 K, indicating superconductivity. The results suggest that hole doping is a viable pathway to achieve high-Tc superconductivity, particularly in oxygen-free compounds. This discovery opens new avenues for the development of high-temperature superconductors.